Data entry devices as a general category vary substantially in structure. However, the most known human operated data entry devices provide a plurality of depressible keys coupled to a computer system or the like. Such typical data entry devices include computer keyboards and telephone dialer keypads. Early computer keyboards included an array of alpha-numeric keys and several function keys. Each key carried a designated input data and a fixed key-top label. As the development of computer systems and data entry systems continued however, the sophistication and complexity of input information correspondingly increased. It soon became apparent to practitioners in the art that the solution to increased complexity of data input could not be met by simply increasing the number of keys. In response to this need, practitioners developed data entry devices in which the same keys were capable of being assigned multiple code reflecting the label alteration. These devices are often referred to in the art as key-reassignment and relabeling keyboards.
Such keyboards are used with a plurality of interchangeable overlays which cover the depressible keys and bear visible indications of the input codes assigned to the underlying keys. For example, an overlay for use in a restaurant may provide visual indication of the Sunday menu available. Depressing the key corresponding to an item indicated in the overlay provides a signal which the system responds to ring up the price and identification of the item. Thus, a great deal of information may be provided to the system by depressing of a single key. When an overlay is changed, the operator informs the system by loading a new program or by entering an overlay associated code.
While such multiple overlay systems provide some improvement in the flexibility and complexity of data entry devices, they are also subject to limitations in terms of the amount of input information which can be processed efficiently. To meet the further increased needs, practitioners in the art have developed multiple paged data entry devices in which a number of sheet overlays may be interchangeably used for manual relabeling and automatic key-reassignment. One such device is set forth in U.S. Pat. No. 4,661,976 entitled AUTOMATIC TELEPHONE DIALER UTILIZING AN ELECTRONIC TELEPHONE BOOK issued Apr. 28, 1987 to Basch. It comprises an automatic telephone dialer in which a plurality of sheets are supported upon a common base. Each sheet includes a plurality of telephone listings. An optical sensing array detects the open sheets of the sheet array. The information indicating the open sheets is provided to the system for key-reassignment.
A somewhat similar device is set forth in the February 1985 issue of the publication entitled HIGH TECHNOLOGY in an article at page 69 thereof written by Cary Lu.
While the foregoing described prior art devices provide key-reassignment and relabeling for data entry devices, they are subject to generally several disadvantages. It has been found for example that such devices tend to be larger than necessary to accommodate one optical detector for each sheet. In addition, the optical detectors and their high power consumption render the production of slim design or pocket model data entry devices impractical. Furthermore, substantial limitations arise as to the number of pages which can be accommodated and sensitivity of the optical devices to page damaged and ambient light.